FIELD OF THE INVENTION
The invention relates to a pressure protection installation or safety-valve unit for a pressure vessel or pressurized container, particularly for a pressure holding station in the primary loop of a pressurized water reactor.
The operating pressure, for instance approximately 155 bar, prevailing in the primary loop of a pressurized water reactor must not be substantially exceeded, if an overload on primary loop components are to be avoided in the event that heat liberated in the interior of the reactor pressure vessel cannot be dissipated by coolant to a sufficient extent.
In order to keep the pressure within the primary loop below the allowable maximum pressure of approximately 170 bar, for instance, so-called pressure holding stations are provided, which include a pressure holder that is connected to the primary loop and is also connected to a blowoff line, through a valve assembly. As a rule, the fixture is a safety valve actuated by the medium located in the pressure vessel. To that end, the safety valve may be opened by a piston that is disposed displaceably in a cylinder which can be acted upon by pressure. The imposition of pressure is performed through a pressure bleeding line that is connected to the pressure vessel and is connected through a control valve to the control chamber of the cylinder. Through this pressure bleeding line, if needed, the static pressure prevailing in the pressure vessel is conducted to the piston of the safety valve when the control valve is open and brings about an opening of the safety valve.
The internal pressure of the pressure vessel always prevails in the pressure bleeding line. In the event of a response, the control line disposed between the control valve and the safety valve cylinder is additionally acted upon by high pressure. For the sake of redundancy, a plurality of independently operating control valves, for instance four of them, are provided for one safety valve. However, the pipelines required for that purpose represent an additional risk factor in the event of an explosion.